The present invention relates to a disc filtration device and the assembling and maintenance methods therefor.
Among the devices used for the liquid/solid separation of a loaded suspension on an industrial scale, large diameter discs more particularly exist which are provided with a rim capping and rigidifying a plurality of filtering sectors by surrounding them. Such sectors are generally covered with a cloth and provided with pipes which are likely to be connected to the external wall of a rotating central shaft by opening into internal outlet channels for the filtered liquid. Such discs are vertically positioned and rotated, with their lower parts being immerged in tanks containing the suspensions to be filtered, whereas the internal channels of the shaft are successively depressed and pressurized to detach the solid fraction, also called cake.
The sectors are fixed to the shaft by various means among which the one consisting in engaging the outlet pipes thereof provided with a tip into the holes of a ring integral with the shaft, and in engaging the tips thereof into the offtakes of the external part of said shaft which open into said internal channels. A rubber sleeve generally provides the sealing of the connection between the pipes and the offtakes. A notch in the holes of the ring makes it possible to pass a pin integral with the sector pipe which, after a quarter turn, is caught by said ring and holds the sector in correct position.
Such devices are more particularly described in document FR 2 779 973. But the construction of such devices raises the problem of positioning tolerance of the pin of the pipe in the sectors which are consequently exposed to a risk of mechanical deformation. This risk is all the higher since the rotation thereof during the quarter turn required for the positioning thereof is forced. The problem of holding curvilinear elements composing the rim during the assembling thereof, which consequently becomes difficult and is exposed to risks of dismounting before all the elements are connected together, also arises.
Another drawback lies in the utilisation of threaded screws in the rim to wedge the sectors therebetween. Such screws do not make it possible to master the stresses caused on the sectors as well as on the rim nor to distribute the same appropriately over the whole disc. Now, such stresses cause deformations or even breaks in the sectors as well as in the rim. Such drawback is all the more tangible when it concerns the construction of very large discs which must, however, have a light structure required for the manual assembling of the sectors. In addition, such prior devices do not allow an easy maintenance because the replacement of only one or several used or damaged filtering sectors requires the dismounting of the rim to extract the pipe of the sector from the embedding thereof in the shaft.
The present invention aims at solving the technical problems raised by the devices of the prior art by offering simple, quick and rational methods for assembling and dismounting the sectors. This goal is reached, according to the invention, by using a filtration device, characterised in that said rim is provided with holes intended to receive each a detachable connection flange bearing, on the one hand, a radial spacer positioned between two adjacent sectors to provide the respective wedging thereof and, on the other hand, cooperating with a quick spring coupling to lock the loaded spacer between the sectors. According to an advantageous characteristic, the filtering sectors are accommodated in triangular pockets made of a filtering cloth, the external edges of which are folded on either side of the sector and fixed using cloth clips. According to another advantageous characteristic, said cloth clips include side flanks forming jaws and at the longitudinal ends thereof elastic lugs bordering said sectors.
Such lugs cover the folds formed at the angle of the pocket for which a sufficient space has been provided by slightly cutting the angles of the sector. The pockets covering the sectors are then slightly closed on the external edge thereof by the spring effect cloth clips which provide a simple, efficient and secure closing without having to use seaming or any other cumbersome method. According to a particular embodiment, said sectors include a structure mounted inside a frame and supporting the filtering cloth. Preferably, the jaws of the cloth clips rest on the structure only and do not extend up to the frame.
According to another embodiment, said rim is composed of a U-shaped section, the branches of which are oriented outwards and the width of which is much greater than the thickness of the sectors. The branches of the U are turned outwards and not towards the inside of the disc so as not to be an obstacle when discharging of the cake. The width of the rim makes it possible to increase the rigidity of the disc on the one hand, and to cause the stirring of the suspension on the other hand. Advantageously, said rim is formed by the assembling of several curvilinear section elements placed end to end and preferably of eight section elements.
According to still another advantageous characteristic, the device includes a ring composed of a fixed part integral with said shaft and a detachable part which, after being assembled, define, at a distance from said offtakes, brackets intended to support the ends of the sectors. Preferably, the detachable part of the ring is divided into several independent elements each including a clamp which provides the final locking of the sectors after the assembling. According to another characteristic, the connection flange has dimensions enabling same to slide into the orifice of said rim to cap the external edge of two adjacent sectors so as to adjust same and connect same to the rim.
A quick coupling is provided made of two hairpin-like rods resting on the spacer of the flange and the looped end of which is engaged into a slot of the rim, whereas the free ends thereof carrying hooks are introduced into and locked in openings provided in said rim. The quick coupling thus forms a spring engaged in various orifices provided in the rim on either side of the housing of the connection clamp, on which such spring applies a measured pressure upon the locking operation. The simultaneous action of the elastic lugs, the cloth clips and the V-shaped spacer of the connection flange and the spring effect quick-coupling, limits the overstress which might damage the sectors and deform the rim.
Another object of the invention is a method for assembling and maintaining a filtration device of the above-described type. The method of the invention provides that the supporting ring is made of two parts, one of which is integral with the shaft and the other is detachable, that a series of spokes providing the support for the rim are mounted on the offtakes of the shaft and on the fixed part of the ring, that the rim is fixed on the ends of adjacent spokes inside the rim and that said spokes are successively replaced by the sectors up to the completed filling of the disc. The assembling of the rim on the spokes is provisional and makes it possible to provide stability to the disc prior to and during the assembling of the sectors. In addition, it is provided to fix the rim on the spokes by simultaneously assembling curvilinear elements positioned end to end.
According to an alternative implementation, a peripheral holding ring is first fixed on said pipes, which is intended to cooperate with notches provided on said fixed or detachable parts of the supporting ring. The holding ring slides into the ring and supports, for the whole rotation of the disc, the weight of the sector which is thus not reported onto the rim.
According to a characteristic of the method, the sectors are installed by bringing them parallel to the disc plane, with the tips thereof being introduced into the offtakes with a slight inclination with respect to said plane, while folding the same in the rim and engaging the pipes into the ring, the sectors are locked on the rim through connection flanges and quick couplings, then the detachable part is assembled to the fixed part of the ring. The sectors are then held by the rim using connection clamps applied and locked with quick spring couplings. Finally, the elements of the detachable part of the ring are connected to the part integral with the shaft by clamps providing the final locking of the whole disc and thus preventing the coning thereof.
According to another alternative embodiment specific to the maintenance, the detachable part of the ring is disengaged, the connection flanges corresponding to the sectors to be replaced are released, then the sectors are removed one after the other by slightly inclining the same and taking the tips out of the offtakes, while installing simultaneously and at the same time new sectors so that the rim (2) remains permanently supported. The device of the invention allows an easy maintenance of the filtration facility by enabling the replacement of a sector independently of the others and this without any quarter turn or dismounting of the rim.
In addition, the method of the invention thus eliminates the risks of falls for the rim elements or deformation of the sectors upon the steps of filling of the disc by providing a stable mechanical behaviour of the latter prior to the mounting of said sectors and by enabling the positioning thereof without requiring the quarter turn to lock it in the ring. Thus, mounting operations can be carried out by only one operator. The rim is thus mounted once and for all. Thanks to the new fixation and locking mode of the sectors which releases the rim not only from the weight of the sectors and the filtration cakes thereof, but also from any accidental mounting mechanical constraints, thanks more particularly to a quick spring coupling, the rim thus transfers to the disc a greater rigidity and a better behaviour which are all the more required as the disc has large dimensions.